The invention relates to saw blades of the type used for cutting metal work pieces, such as band saw blades and hack saw blades.
Conventional band saw blades are formed with teeth of uniform size and pitch throughout with alternate teeth being bent outward relative to the plane of the blade. Conventionally set band saw blades are characterized by uneven side-to-side tooth set which causes crooked cutting and non-symmetrical cutting forces on the teeth, which cause vibration, noise and wear. Also, when conventional band saw blades are used to cut large sections of metal, the blades may be subjected to bending or setting of the teeth. Thus, band saw blades with teeth of uniform size and pitch throughout are subject to increased wear, thereby shortening the lifetime of the blades.
An improved band saw blade is disclosed in U.S. Pat. No. Re. 31,433. The band saw blade has an arrangement and form of teeth designed to reduce vibration, cutting noise and chatter and to enhance cutting speed and blade life. Cutting teeth are alternately arranged in recurrent groups in which each group comprises a series of different teeth. The teeth in each group differ from each other in size, pitch, and angle of bend, and also in rake angle. The outer tips of all of the teeth are in substantial alignment, the difference in size of the teeth being attained in the variations in the depth of the gullets.
A further attempt to realize a band saw blade characterized by improved cutting rate and extended life is disclosed in U.S. Pat. No. 4,292,871. The band saw comprises a plurality of saw teeth of hard metal which are welded to a base portion of a strong flexible material. Rake angles and relief angles are selected to define a saw tooth geometry having a positive rake angle with increased tooth mass while maintaining a large gullet space to provide good chip removal along with strong tooth tip configuration and a large heat transfer tooth mass to enhance cutting rate and blade lifetime. However, the high temperatures, in the order of 2600.degree. F. required for fusion welding result in thermal stresses in the weld zone which ultimately contribute to failure of the weld because of the constant bending of the band saw blade around a lateral axis during its rotation, and the carbide tips may break off reducing the lifetime of the saw blade. Also, a hard metal piece broken off in this way will often become embedded in the cut causing damage to following teeth of the saw blade as well.
One attempt at solving this problem is disclosed in the European patent Application, published June 30, 1982. This application discloses a band saw blade fitted with hard metal plates which are soldered onto the blade body. With this arrangement, the thermic stresses are largely contained in the intermediate soldering layer. However, because band saw blades have a relatively small body thickness, typically in the order of 0.062 inches, any chips carried by the blade back into the cut could tend to deflect the band saw tooth laterally into the side of the material being cut. Such lateral deflection of the tooth results in a twisting torque on the carbide tip causing both compressive and tensive stresses on the joint which could ultimately result in failure of the joint if the tensile strength of the soldered joint is exceeded.
It is the nature of triple-chip bandsaw cutting to remove a chip which more closely resembles a milling chip, which is longer and thicker than is generated by a conventionally set blade. It is the combination of the heavy chip and the zero clearance between the carbide tooth and the kerf which forces the tooth to displace laterally. The dynamic forces on the tooth during entry into the cut, which are transitory in nature, are capable of dislodging the tooth from the blade. Once the tooth has successfully entered the cut, it is no longer vulnerable to damage other than normal wear. This condition was not recognized or anticipated as being the fundamental weakness of the blade. Although bandsaw machines are normally fitted with brushes to remove the chips, they are in general practice not adequately maintained or properly used and chip carry over is very common.
While these improved band saw blades address to some extent blade vibration and useful lifetimes, it is desireable to have a band saw blade which achieves high cutting rates, straight cuts, and extreme smoothness of the cut surface while maintaining long blade life and which is capable of cutting large sections of metal with accuracy unattainable using conventional blades with set teeth.